Such a data carrier and such a circuit, such a communication device as well as such a method have been developed by the applicant and have been put onto the market, respectively, as a chip card and a read/write device for such a chip card under the designation MIFARE and are consequently known.
The known data carrier and the known communications device have the problem that writing information data into memory means of the data carrier is possible on in the course of bi-directional communication process. In the process of this bi-directional communication the communication device first performs an explicit selection of a data carrier, during which data is exchanged between the data carrier and the communication device. Subsequent to the selection of the data carrier. This starts a lengthy process between the data carrier and the communication device, in which process first of all an addressed memory location of the memory means is initialized for the storage of the information data. During the initialization a copy of the memory data stored in the addressed memory location is made and subsequently a read-after-write check of this copy is carried out. When the read-after-write check of this copy is successful the memory data stored in the addressed memory location is erased. After the erasure the information data transferred to the data carrier and received by the data carrier is loaded into the addressed memory location and this forms new memory data. A new read-after-write check of the memory data is preformed. When the new read-after-write check is successful the bi-directional communication between the data carrier and the communication device is terminated and the selection of the data carrier is canceled. This process provides maximal data security. However, the process less advantageous for an application in which information data should be written into memory means of plurality of data carriers substantially simultaneously during a communication process between the data carriers and the communication device, because in such applications it is often impossible to assure than an explicit selection of each data carrier and a time-consuming read-after-write check can be achieved for one hundred percent. This limitation is particularly important when a plurality of data carriers rapidly pass through a communication range of the communication device or when data carriers move past the communication device at the border of the communication range. In both cases a minimum dwell time required for a reliable bi-directional communication is difficult to achieve, as a result of which loss of data owing to a premature termination of a communication process is not unlikely.
It is an object of the invention to solve the afore-mentioned problems with a data carrier of the type defined in the opening part of claim 1, with a circuit of the type defined in the opening part of claim 4, with a communication device of the type defined in the opening part of claim 7, and with a method of the type defined in the opening part of claim 10, and to provide an improved data carrier, an improved circuit, an improved communication device and an improved method, so as to guarantee a reliable writing of information data into the memory means, without the risk of data loss, even for applications where in the process of communication between a communication device and at least one data carrier no explicit selection of the data carrier as during the bidirectiona communication and no time-consuming read-after-write check have been provided.
By the provision of the characteristic features in accordance with the invention it is achieved in an advantageous manner that a unidirectional communication from a communication device to a data carrier is possible, during which the information data can be written into the memory means of the data carrier communication very rapidly and without the risk of a data loss, without the explicit selection of the data carrier and without the time-consuming read-after-write check.
Moreover, the major advantage is obtained that even during a communication process with a plurality of data carriers the information data can be written into the memory means of each data carrier in a very rapid manner and, above all, simultaneously.
The provision of the characteristic features defined in claim 2, claim 5, claim 8 and claim 11, respectively, has the advantage that even during the unidirectional communication a passive selection is possible, during which passive selection each data carrier can decide autonomously on the basis of the memory means initialized in accordance with the group data whether the information data should be loaded into its memory means initialized in accordance with the group data.
The provision of the characteristic features defined in claim 3, claim 6, claim 9 and claim 12, respectively, has the advantage that an optimum utilization of the memory means available in the data carrier is possible. Furthermore, the advantage is obtained that a highly flexible structure of the group data is possible, which flexible structure enables a highly versatile use of the data carrier to be achieved, which is advantageous particularly in the case of varying requirements in different fields of use.
The above-mentioned as well as further aspects of the invention will become apparent from the embodiments described hereinafter by way of example and will be elucidated with reference to these examples.